1. Field of the Invention
The present invention relates to a method and apparatus for correcting air-flow sensor output and adapting a data map used to control engine operating parameters; and more particularly, to a method and apparatus for correcting air-flow quantities output by an air-flow sensor and to a method and apparatus for adapting a data map storing correction values used to correct detected air-flow quantities.
2. Description of Related Art
The majority of vehicles produced are controlled using an electronic control unit (ECU). The ECU controls such engine functions as fuel injection quantity and ignition timing. Typically, the ECU receives a plurality of sensor inputs to determine the engine operating conditions, and based thereon controls respective components of the engine to produce a desired fuel injection quantity, ignition timing, etc.
Systems which control the air/fuel ratio (A/F ratio) do so based upon the output of an air-flow sensor, typically a hot film air-flow meter, and an oxygen sensor positioned in an exhaust passage of the engine. U.S. Pat. No. 4,962,741 to Cook, hereby incorporated by reference, discloses such a device. As disclosed in Cook, a base fuel injection quantity is determined based on the air-flow quantity detected by the air-flow sensor. This base injection quantity is then regulated based on the oxygen sensor output to perform a fine fuel metering and obtain a stoichiometric A/F ratio. Specifically, a lambda regulation value is calculated based on the oxygen sensor output, and the base injection quantity is altered in accordance with the lambda regulation value. A/F ratios above the stoichiometric value result in rich combustion, and A/F ratios below the stoichiometric value result in lean combustion. For certain desired operating conditions, the engine is controlled to achieve lean or rich combustion. Unfortunately, if the air-flow quantity indicated by the air-flow sensor output differs from the actual air-flow quantity, then fuel injection, ignition timing, etc., may be improperly controlled. For instance, if ignition timing is improperly advanced, the engine may knock. In the Cook patent, the basic injection quantity is further refined to obtain fuel injection control signals corresponding to the fuel injector for each cylinder and to control the A/F ratio of each cylinder.
FIG. 1A illustrates the air-flow quantities output by an air-flow sensor with respect to engine RPM when the engine is operating under a high load. FIG. 1B illustrates the actual air-flow quantities under the same conditions. As a comparison of FIGS. 1A and 1B indicates, the output from the air-flow sensor at low RPM and high load engine conditions is distorted. Accordingly, under these engine conditions, fuel injection, ignition timing, etc. will not be properly controlled.
When the detected air-flow quantity reflects the real air-flow quantity, the lambda regulation value, approaches a value of 1 such that the base injection quantity is not altered. When, however, the detected air-flow quantity is less than or greater than the real air-flow quantity, the lambda regulation value becomes greater than or less than 1, respectively, to correct errors in the base injection quantity caused by the erroneously detected air-flow quantity. Unfortunately, during transient engine operating conditions, the lambda regulation value cannot be accurately determined.
As an alternative or additional correction technique, some ECU's store an air-flow correction map of fixed correction factors. During engine production, the differences between the detected and actual air-flow quantities are tested for a variety of engine conditions. Each engine condition is referenced by the engine RPM and the throttle opening degree. A proper correction factor is then coded into the air-flow correction map for each RPM and throttle opening degree pair.
During operation, the ECU addresses a correction factor from the air-flow correction map based on the engine RPM and throttle degree opening, and multiplies the detected air-flow value by the correction factor to produce a corrected air-flow quantity.
The air-flow correction map is produced using a test engine, and then this map is stored in the ECU's memory for the engines produced during mass production. Unfortunately, engine operating conditions vary from engine to engine and vehicle to vehicle. While the air-flow correction map helps produce reliable air-flow quantities for the test engine, this may no: be the case for the engines produced during mass production. Accordingly, to develop reliable air-flow correction maps for each engine would require performing a test routine for each engine. This technique, however, is not practical in mass production.